DMSO: An Efficient Catalyst for the Cyclopropanation of C60, C70

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DMSO: an efficient catalyst for the cyclopropanation of C60, C70, SWNTs and graphene through the Bingel reaction Bo Jin, Juan Shen, Rufang Peng, Congdi Chen, Qingchun Zhang, Xiaoyan Wang, and Shijin Chu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie504918f • Publication Date (Web): 12 Feb 2015 Downloaded from http://pubs.acs.org on February 14, 2015

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DMSO: an efficient catalyst for the cyclopropanation of C60, C70, SWNTs and graphene through the Bingel reaction Bo Jin, *†,‡ Juan Shen, ‡ Rufang Peng, *†,‡ Congdi Chen, ‡ Qingchun Zhang, ‡ Xiaoyan Wang § and Shijin Chu † †

State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology, Sichuan Mianyang 621010, China ‡

Department of Chemistry, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China §

Analytical & Testing Center, Sichuan University, Chengdu 610064, China

Address correspondence to Bo Jin and Ru-Fang Peng, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang, Sichuan, 621010, China. Fax: (+86)-816-2419011; E-mail: [email protected], [email protected] Graphic for manuscript O R

O

O

O

R

O R

O

O

O

RRO O

O

O

R

R = CH2CH3

O

R O

O O

R1

Na2CO3/DMSO Graphene rt, 15 min

R

R1

C70 Na2CO3/DMSO 0 oC, 5 min

C60

Br

Na2CO3/DMSO 10-20 oC, 2-10 min

R2

R1, R2 = COOR, ArCO, CN, RCO, (RO)2PO 34 examples, up to 68% yield

Na2CO3/DMSO SWNTs rt, 15 min

6 examples, up to 47% yield

O R

O

O

R2

O

O

RR O O

O

RR

O O

O O

R

R = CH2CH3

ABSTRACT: Dimethyl sulfoxide (DMSO) with sodium carbonate (Na2CO3) is an effective catalyst system for C60 cyclopropanation through the Bingel reaction. Various bromomalonic esters, brominated β-keto esters, brominated 1,3-diketones, and other bromo-substituted active methylene compounds can react with C60 in the presence of DMSO and Na2CO3 to achieve excellent yields of the corresponding methanofullerenes at 10 °C. 1


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Moreover, this proposed methodology has been also employed successfully to functionalize [70]fullerene, single walled carbon nanotubes (SWNTs) and graphene. This protocol is beneficial because it involves short reaction time, high yield, and a simple procedure. Additionally, this method does not need a strong base, such as sodium hydride and 1,8-diazabicyclo[5,4,0]undec-7-ene. Inexpensive Na2CO3 can be the catalyst. INTRODUCTION [60]Fullerene derivatives are attractive compounds because of their outstanding properties and potential applications in medicinal chemistry and material sciences 1-8. Since the large scale availability of fullerenes in the 1990s, various reactions have been developed to prepare fullerene derivatives 9-15. One such reaction is fullerene cyclopropanation involving reaction with bromomalonate in the presence of a base, which is known as the Bingel reaction

16

. The Bingel reaction generally requires a strong base, such as 1,8-diazabicyclo[5,4,0]undec-7-ene

(DBU) and sodium hydride (NaH), as a catalyst, which is conducive for carbanion formation through bromo-active methylene deprotonation

16-27

. Therefore, a methanofullerene derivative containing an acidic or

base-labile group cannot be directly synthesized using this method

28-32

. In addition, NaH is sensitive to water,

thus anhydrous reaction conditions are necessary. Although a reaction with DBU, instead of NaH, as the catalyst does not require anhydrous conditions and provides higher yield, DBU can react with fullerene through chemical complexation

33

. DBU dosage affects yield, such that higher or lower quantity of DBU significantly decreases

yield. Therefore, other mild catalysts for the Bingel reaction are still required. The authors recently attempted to complete [60]fullerene cyclopropanation through the Bingel reaction without NaH or DBU as the base. With the inexpensive sodium carbonate 34 (Na2CO3) as base and the mixture of dimethyl sulfoxide (DMSO) and chlorobenzene (PhCl) as solvent, [60]fullerene was found to easily react with bromo-substituted active methylene compounds. Additionally, almost all substrates achieved good yields of the desired monoadduct methanofullerenes under mild reaction conditions for a few minutes.

2



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RESULTS AND DISCUSSION Hirsch

10, 35, 36

states that the Bingel reaction is a two-step process (Scheme 1). In the first step, the

bromo-substituted active methylene compound strips protons under strongly alkaline conditions to generate a carbanion. Then, carbanion reacts with fullerene to obtain an intermediate carbanion that undergoes ring closure with displacement of bromide. Among these events, the rate is determined by the deprotonation of the bromo-substituted active methylene compound. DMSO can react with alkyl/aryl halide to form the dimethylalkoxynsulfonium salt intermediate

37-40

, which can easily be deprotonated under weak alkaline

conditions. Na2CO3 is an inorganic weak alkaline, which has been was successfully utilized to replace DBU in the Bingel reaction employing diethyl bromomalonate under the mechanochemical ‘high-speed vibration milling’ conditions.

41, 42

So we tried to synthesize methano[60]fullerenes through a [60]fullerene and

bromo-substituted active methylene compounds reaction using DMSO and Na2CO3 as the catalyst. The reaction of [60]fullerene with diethyl bromomalonate was first examined (Scheme 2). The yields of methanofullerene 1 under different conditions are summarized in Table 1.

O

O R

O

O

R

-H

Br

O

O

DBU or NaH

R

+

O

O

R

Br C60

O O

O

O Br O R

O -Br

O

-

Scheme 1. General mechanism of the Bingel–Hirsch reaction.

3


O

R

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O

O O +

O

O

O O

Na2CO 3 PhCl/DMSO

O Br

1 Scheme 2. Synthesis of methanofullerene 1. Table 1. Optimization of reaction conditions. Entry

Catalyst

Solventa)

Time (min)

Temperature (°C)

Ratiob)

Yield of 1 (%)c)

Recovered C60 (%)

1

Without Catalyst

PhCl/DMSO (2:1)

10

10

1:2

0

100

2

Na2CO3

PhCl

10

10

1:2:4

0

100

3

Na2CO3

PhCl//DMSO (2:1)

5

10

1:2:4

26(98)

74

4

Na2CO3

PhCl//DMSO (2:1)

5

10

1:6:12

39(96)

59

5

Na2CO3

PhCl/DMSO (2:1)

5

10

1:12:24

53(92)

43

6

Na2CO3

PhCl/DMSO (2:1)

5

10

1:20:40

68(88)

23

7

Na2CO3

PhCl/ DMSO (2:1)

5

10

1:30:60

65(78)

17

8

K2CO3

PhCl/DMSO (2:1)

5

10

1:20:40

24(93)

74

9

NaHCO3

PhCl/DMSO (2:1)

5

10

1:20:40

10(98)

89

10

Li2CO3

PhCl/DMSO (2:1)

5

10

1:20:40

45(88)

49

11

NaOAc

PhCl/DMSO (2:1)

5

10

1:20:40

12

NaOAc

PhCl/DMSO (2:1)

5

-5

1:2:4

14(15)

7

13

NaOAc

PhCl/DMSO (10:1)

5

-5

1:1.2:4

54(65)

16

0

14

Na2CO3

PhCl/DMSO (2:1)

5

10

1:20:10

59(89)

34

15

Na2CO3

PhCl/DMSO (2:1)

5

10

1:20:60

68(87)

22

16

Na2CO3

PhCl/DMSO (4:1)

5

10

1:20:40

44(93)

53

17

Na2CO3

PhCl/DMSO (3:2)

5

10

1:20:40

66(84)

21

18

Na2CO3

PhCl/DMSO (2:1)

5

-5

1:20:40

53(94)

44

19

Na2CO3

PhCl/DMSO (2:1)

5

5

1:20:40

61(90)

32

20

Na2CO3

PhCl/DMSO (2:1)

5

20

1:20:40

63(76)

19

21

Na2CO3

PhCl/DMSO (2:1)

2

10

1:20:40

32(95)

66

22

Na2CO3

PhCl/DMSO (2:1)

10

10

1:20:40

61(75)

19

Toluene

6.5 h

Room temp.

1:1.5:10

45

- f)

57

- f)

23 24 a)

0

d)

NaH

16

DBU

27

Toluene

6.0 h

Room temp.

e)

1:1.5:1.5:3

Volume ratio of PhCl : DMSO in parentheses; b)molar ratio of C60 : diethyl bromomalonate : inorganic base; c)isolated yield, the

yield in parentheses was based on consumed C60; d)The reaction was very fast, and no unreacted C60 and monoadduct product 1 were obtained; e) molar ratio of C60 : diethyl malonate : CBr4 : DBU; f) no literature data.

Methanofullerene 1 was obtained with a 26% yield when [60]fullerene (0.05 mmol), diethyl bromomalonate (0.1 mmol), and Na2CO3 (0.2 mmol) were added to 20 mL of PhCl and 10 mL of DMSO binary mixture and 4



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stirred at 10 °C for 5 min (Table 1, entry 3). No reaction occurred without a catalyst or DMSO in the solvent (Table 1, entries 1 and 2). Higher proportions of diethyl bromomalonate (material ratios 1:6, 1:12, 1:20, and 1:30) were used to improve methanofullerene 1 yield. As shown in Table 1 (entries 3–7), highest yield was obtained at the material ratio of 1:20. Diethyl bromomalonate proportions above 1:20 did not improve the result. The effect of other inorganic bases on the model reaction was also investigated (Table 1, entries 6 and 8–13). Na2CO3 provided the best result. Low yield was obtained using the inorganic bases, K2CO3, NaHCO3, and Li2CO3. No methanofullerene 1 was obtained and almost all products were multi-addition products when NaOAc, instead of Na2CO3, was used as the base (Table 1, entry 11). Moreover, different Na2CO3 and DMSO proportions were also tested to increase the methanofullerene 1 yield. The optimum ratio of [60]fullerene, diethyl bromomalonate, and Na2CO3 was 1:20:40, and increasing the amount of Na2CO3 did not significantly affect product yield (Table 1, entries 6, 14, and 15). However, the PhCl and DMSO proportion did significantly affect the yield. The optimal proportion of PhCl and DMSO was 2:1, and lower quantity of DMSO reduced the product yield (Table 1, entry 16). The reaction was performed at -5 °C to 20 °C for 2 min to 10 min to investigate the effects of temperature and reaction time (Table 1, entries 6 and 18–22). The reaction was completed within 5 min at 10 °C, and the methanofullerene 1 yield was 68% (Table 1, entry 6). Prolonging the reaction time and increasing the temperature the product yield was reduced The 68% yield (88% based on consumed C60) of methanofullerene 1 was higher than the previously reported technique, which applied NaH 16 or DBU 22, 27 as the base and only provided 45% and 57% methanofullerene 1 yield respectively (Table 1, entry 23-24). Moreover, the reaction time was reduced from 6.5 h to 5 min when Na2CO3/DMSO, instead of NaH or DBU, was used as catalyst, which indicates the efficiency of the proposed catalyst system. A plausible reaction mechanism is proposed (Scheme 3). Nucleophilic attack by dimsyl anion on the brominated α-carbon atom and concomitant bromine departure leads to the dimethylsulfoxonium intermediate I.

37-40

The dimethylsulfoxonium intermediate I could easily strip protons under weak alkaline to generate 5


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carbanion intermediate II because dimethylsulfoxonium has a stronger electron withdrawal ability than bromine (Pauling's electronegativity values for oxygen and bromine are 3.44 and 2.96, respectively). Next, carbanion intermediate II reacts with fullerene to obtain a charged intermediate III and intramolecular displacement of dimethyl sulfoxide provides cyclopropanation product IV.

Scheme 3. Plausible reaction mechanism of the Bingel reaction using the proposed Na2CO3/DMSO catalyst system. Various bromo-substituted active methylene compounds, such as bromomalonic esters, brominated β-keto esters, and brominated 1,3-diketones were employed to examine the generality and scope of the proposed methodology. First, [60]fullerene cyclopropanation with various bromomalonic esters were investigated under standard conditions. The reactions of [60]fullerene and bromomalonic esters 2a–j are shown in Scheme 4. When [60]fullerene was treated with 20 equiv bromomalonic esters 2a–j and 40 equiv Na2CO3 in a PhCl/DMSO binary mixture solvent at 10 °C for 5 min, the corresponding methanofullerene derivatives 3a–j were obtained in 29%–68% yields (68%–87% based on consumed C60).

6



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O R O

O R

+

O

R

O

O

O

O

R

Na2CO3 PhCl/DMSO

Br

2a-j 2a, 3a: R = CH3; 2c, 3c: R = CH 2CH2Cl; 2e, 3e: R = CH2CH2Ph; 2g, 3g: R = 4-PyCH2; 2i, 3i: R = 4-ClPhCH 2;

3a-j

2b, 3b: R = CH(CH3)2; 2d, 3d: R = CH2CH2OCH2CH2Cl; 2f, 3f: R = CH2Ph; 2h, 3h: R = 4-NO2PhCH2; 2j, 3j: R = 4-(i-Pr)PhCH2;

Scheme 4. Cyclopropanation of C60 with bromomalonic esters 2a–j.

O

O O

O

O +

O

R

R

Na2CO3 PhCl/DMSO

Br 4a-g 5a-g 4a, 5a: R = CH2CH2Cl; 4b, 5b: R = CH 2CH2OCH3; 4c, 5c: R = CH2CH2OCH2CH 2Cl; 4d, 5d: R = 4-CH3OPhCH2; 4e, 5e: R = 4-NO2PhCH2; 4f, 5f: R = 4-ClPhCH2; 4g, 5g: R = 4-(i-Pr)PhCH2; Scheme 5. Cyclopropanation of C60 with bromo acetoacetyl esters 4a–g. Then, the reaction of the bromo acetoacetyl esters and aromatic ethyl bromoformylacetates with [60]fullerene was examined under standard conditions. During the reaction of [60]fullerene with bromo acetoacetyl esters 4a–g, good yields of monoadduct cyclopropanation products were obtained (Scheme 5). The corresponding cyclopropanation products 5a–g were obtained in 34%–63% yields (60%–84% based on consumed C60) when a mixture of [60]fullerene, 20 equiv acetoacetyl esters 4a–g and 40 equiv Na2CO3 was dissolved in 30 mL of a PhCl/DMSO mixed solvent and stirred at 10 °C for 5 min. Analogous observations were also made on the 7


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cyclopropanation of [60]fullerene with aromatic ethyl bromoformylacetates 6a–g. As shown in Scheme 6, the corresponding cyclopropanation products 7a–g were obtained in 43%–66% yields (76%–88% based on consumed C60) under optimal conditions.

O

O

Ar O

+

O

O

Ar

Na2CO3

O

PhCl/DMSO

Br 6a-g

7a-g 6a, 7a: Ar = Ph; 6c, 7c: Ar = 4-CH3Ph; 6e, 7e: Ar = α-Naphth; 6g, 7g: Ar = 2-Thiophene;

6b, 7b: Ar = 4-CH3OPh; 6d, 7d: Ar = 4-ClPh; 6f, 7f: Ar = 2-Furan;

Scheme 6. Cyclopropanation of C60 with aromatic ethyl bromoformylacetates 6a–g.

Finally, the bromo-substituted active methylene compounds containing other electron-withdrawing substituents in the methylene moiety were examined. Reactions of substrates 8a–8i with [60]fullerene were conducted to produce the desired product 9a–i in 26%–64% yields (Table 2, 63%–96% yields based on consumed C60). Only one monoadduct cyclopropanation product 9a was obtained when α,γ-dibromo ethyl acetoacetate 8a was used as the cyclopropanation reagent. Similar results were also obtained for α,γ-dibromo β-keto esters 8b–d, which indicates that the activity of methylene proton plays a critical role in this reaction, and the Na2CO3/DMSO catalyst system has excellent chemical selectivity for the [60]fullerene cyclopropanation reaction. Moreover, the high yield (64%, 90% based on consumed C60) in the diethyl ethoxycarbonylmethano [60]fullerene phosphonate 9i preparation demonstrates the superiority of the new catalyst system over the existing technology, which applies DBU as the base and only produces 9i in a 45% yield after stirring [60]fullerene, I2, and triethyl phosphonoacetate at room temperature for 4 h 30.

8



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Table 2. Cyclopropanation of C60 with bromo-substituted active methylene compounds 8a–i. R R +

Br R'

R'

Na2CO3 PhCl/DMSO

8 9 Entry

O 1

Temperature (oC)

Substrate 8

Br O

O

Br O

O

41 (86)

O

O

Br 8b

3

O

9a

5

10

O

Br

Yield a (%)

Product 9

O

Br Br 8a

2

Reaction time (min)

O

O

9b

5

10

41 (67)

O O O Br

O

Br

O Br 8c

5

10

O

9c

59 (84) O O

O

O Br 8d

Br O

O 10

9d

5

28 (79)

O O

O O

5

Br 8e O

6

Br O

4

10 O

Ph

34 (78)

9e

4

O Ph O

Ph Br 8f

9f

2

10

O

32 (96)

Ph

O NC 7

O Br 8g O

CN 9g

5

10

Br 8

9

Br O

8h

O

OC2H5 P OC H 2 5 OC2H5

35 (78)

9h

5

10

O 9i

10

20

8i

a)

26 (63)

O O

O

O O

O

OC2H5 P OC H 2 5

64 (90)

OC2H5

Refers to isolated yield, the yield in parentheses was based on consumed C60

The mass spectra, 1H NMR,

13

C NMR, FT-IR, and UV–vis spectral data confirmed the product

structures 1, 3a–j, 5a–g, 7a–g, and 9a–j. The product spectral data of 1 16, 3g 43, 9f 44, 9g 45, and 9i 30 were 9


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consistent with previous reports. All products exhibited correct molecular weights in the mass spectra and expected chemical shifts as well as splitting patterns of all the protons in the 1H NMR spectra. The 13C NMR spectra of 3a–j displayed one signal for the two similar carbonyl C atoms in the 162.0 ppm – 163.3 ppm range, 14–17 signals for the 58 fullerene sp2-C atoms in the 138.5 ppm – 145.5 ppm range, and one signal for the two fullerene sp3-C atoms in the 70.80 ppm – 71.65 ppm range. The 13C NMR spectra of 5a–g, 7a–g and 9a–c revealed 25–29 peaks in the 137.5 ppm – 146.5 ppm range for corresponding 58 fullerene sp2-carbon atoms. Meanwhile, 9e and 9h exhibited 15 peaks in the 137.5 ppm – 145.5 ppm range for their 58 fullerene sp2-carbon atoms. The two different carbonyl C atoms of products 5a–g, 7a–g, and 9a–d displayed two signals in the 177.2 ppm –192.3 ppm and 162.2 ppm –164.4 ppm ranges. The two similar carbonyl C atoms of products 9e and 9h appeared at 193.10 and 194.12 ppm, respectively. The two fullerene sp3-carbon atoms of products 5a–g, 7a–g, 9a–e, and 9h appeared in the 71.5 ppm – 74.0 ppm range, and the other sp3-carbon atom in the cyclopropane of products 3a–j, 5a–g, 6a–g, and 9a–i appeared in the 55.0 ppm – 70.5 ppm range. To examine the generality and scope of this proposed methodology for other carbon materials, [70]fullerene, single walled carbon nanotubes (SWNTs) and graphene were used in place of [60]fullerene. The reactions of [70]fullerene and bromomalonic esters 2a–c, 2f and 2j-k are shown in Scheme 7. Usually, there are three different double bonds in the structure of [70]fullerene that can be cyclopropanated to afford corresponding three different isomers (called "type α", "type β" and "type ε" adduct respectively). As shown in Scheme 7, only "type α" adduct was obtained in this reaction, which was consistent with the previously reported results 16. When [70]fullerene was treated with 1.6 equiv bromomalonic esters 2a–c, 2f, 2j-k and 4 equiv Na2CO3 in a PhCl/DMSO binary mixture solvent at 10 °C for 5 min, the corresponding methano[70]fullerene derivatives 10a–c, 10f and 10j-k were obtained in 40%-47% yields (62%-68% based on consumed C70). Product 10k was known compound, and its structure was confirmed by comparison of its 10



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spectroscopic data with those reported in the literature

16, 46

. The structure of products 10a–c, 10f and 10j

were confirmed by their MS, 1H NMR, 13C NMR, FT-IR, and UV-Vis spectrometric and spectroscopic data. The 13C NMR spectra of products 10a–c, 10f and 10j showed only one signal for the two carbonyl carbon atoms and 32-34 signals for the fullerene region (130-160 ppm). It revealed that all the products 10a–c, 10f and 10j have the Cs-symmetrical structures. This improved method has been also employed successfully to functionalize SWNTs (Scheme 8) and graphene (Scheme 9). The introduction of the ester group allowed the SWNTs and graphene to be probed by FT-IR and XPS spectroscopy. The FT-IR spectra showed the change in the chemical structure of the original and modified SWNT and were provided as supplementary information. Compared with the original SWNTs, the new sbsorption peak at 1724 cm-1 in the FT-IR spectrum of modified SWNTs informed the ester group presented in modified SWNTs. The XPS spectra of the original and modified SWNTs were also shown. In latter, the degree of functionalization was estimated to be ca. 3%, see Supporting Information. The FT-IR spectra and XPS spectra of the original and modified graphene were also showed the similar result that the ester group has successfully been functionalized on graphene, and the degree of functionalization was estimated to be ca. 2.5%, see Supporting Information. Compared with the previously reported method for functionalizing graphene and fullerene, the reaction time was reduced from 15 h to 15 min when Na2CO3/DMSO, instead of DBU, was used as catalyst. 47 48 Moreover, the ca. 3% functionalization degree of SWNTs was higher than the previously reported method 47, which applied DBU as the base and procided ca. 2% functionalization degree of SWNTs.

11


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R O

+

R

O

O O R

O

O

O

O

Na2CO3

R

PhCl/DMSO

Br

2a-k

10a-k

2a, 10a: R = CH3; 2b, 10b: R = CH(CH3)2; 2c, 10c: R = CH2CH2Cl; 2f, 10f: R = PhCH 2; 2j, 10j: R = 4-(i-Pr)PhCH2; 2k, 10k: R = CH2CH3

Scheme 7. Cyclopropanation of C70 with bromomalonic esters 2a–c, 2f, and 2j-k.

O O

SWNTs

O

O

O

O

O

O O

O

O O

rt, 15 min

+ O

Na2CO3/DMSO

O

O

O Br Scheme 8

Cyclopropanation of SWNTs with diethyl bromomalonate

O O

Graphene

O

O

O

O

O O

O

O

O O

rt, 15 min

+

Na2CO3/DMSO

O

O

O

O Br

Scheme 9

Cyclopropanation of graphene with diethyl bromomalonate

Conclusion Excellent catalytic activities were found for the cyclopropanation of [60]fullerene, [70]fullerene, SWNTs and graphene with a broad variety of bromo-substituted active methylene compounds using the proposed Na2CO3/DMSO catalyst system. The reactions were conducted under mild reactions for a few 12



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minutes, and almost all the substrates achieved the desired monoadduct products with good yields. These results represent a significant improvement in convenience and yield for the Bingel reaction of fullerenes. Further applications of the proposed methodology to synthesize other functional fullerene derivatives are being investigated. Experimental Section General Procedure for [60]fullerene cyclopropanation using Na2CO3/DMSO catalyst system [60]fullerene (0.050 mmol), Na2CO3 (1.0 mmol), bromo-substituted active methylene compound (1.0 mmol), chlorobenzene (20 mL), and DMSO (10 mL) under air were added to a 50 mL round-bottom flask with a magnetic stirring bar. The reaction was stirred at -5 °C–20 °C for 2 min –10 min. After the reaction was completed, the mixture was poured into 200 mL of water. The organic layer was evaporated under vacuum, and a column chromatography on silica gel purified the residue to obtain the corresponding cyclopropanation products. The reaction time, temperature, and product yields are presented in Supporting Information. General Procedure for [70]fullerene cyclopropanation using Na2CO3/DMSO catalyst system [70]fullerene (0.050 mmol), Na2CO3 (0.2 mmol), bromomalonic esters (0.080 mmol), chlorobenzene (20 mL), and DMSO (10 mL) under air were added to a 50 mL round-bottom flask with a magnetic stirring bar. The reaction was stirred at 10 °C for 5 min. After the reaction was completed, the mixture was poured into 200 mL of water. The organic layer was evaporated under vacuum, and a column chromatography on silica gel purified the residue to obtain the corresponding cyclopropanation products. The reaction time, temperature, and product yields are presented in Supporting Information. General Procedure for cyclopropanation of SWNTs and grapheme using Na2CO3/DMSO catalyst system

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10 mg SWNTs or graphene was suspended in 20 mL chlorobenzene and 10 mL DMSO by ultrasonic treatment for 15 minutes. Then 166.0 mg Na2CO3 (2.0 mmol) and 578 mg diethyl bromomalonate (2.0 mmol) were added to the reaction vessel. The reaction mixture was stirred for 15 min under room temperature. After the reaction was completed, 200 mL water was added to quench the reaction. Then the reaction mixture was centrifuged at 4000 rpm for 30 minutes. The supernatant was discarded and the solid remainder was made up to 50 mL with ethanol. The solid-liquid mixture was separated by centrifugation under identical conditions, and the supernatant was again discarded. The obtained solid product was washed with 3 × 50 mL of ethanol, and then dried at 80 ºC overnight to afford the cyclopropanation product of SWNTs or graphene. Acknowledgements We are grateful for financial support from the National Natural Science Foundation of China (Project No. 21301142, 21201142, 51372211), National Defense Fundamental Research Projects (Project No. A3120133002), Youth Innovation Research Team of Sichuan for Carbon Nanomaterials (2011JTD0017), Applied Basic Research Program of Sichuan Province (2014JY0170) and Southwest University of Science and Technology Researching Project (13zx9107). Supporting Information Available.

The detailed synthesis process of 1, 3a-j, 5a-g, 7a-g, 9a-i and 10a-k, and their 1H NMR and 13C NMR spectra. This material is available free of charge via the Internet at http://pubs.acs.org.

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DMSO: An Efficient Catalyst for the Cyclopropanation of C60, C70

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